Manual MRIK3-C EN
Woodward
DOK-TD-MRIK3-C Rev. A
67
7.4.2
Checking the operating and resetting values of the relay
Inject a current which is less than the relay set values in phase 1 of the relay and gradually in-
crease the current until the relay starts, i.e. at the moment when the LED I> and L1 light up or the
alarm output relay I> is activated. Read the operating current indicated by the ammeter. The devia-
tion must not exceed 3% of the set operating value or 1% In.
Furthermore, gradually decrease the current until the relay resets, i.e. the alarm output relay I> is
disengaged. Check that the resetting current is smaller than 0.97 times the operating current.
Repeat the test on phase 2, phase 3 and earth current input circuits in the same manner.(Accuracy
of earth current measuring
3% of measuring value.
7.4.3 Checking the relay operating time
"For this test the AR function should be deactivated. The number of automatic reclosing attempts
"SHOT" should be set to "EXIT".
To check the relay operating time, a timer must be connected to the trip output relay contact. The
timer should be started simultaneously with the current injection in the current input circuit and
stopped by the trip relay contact. Set the current to a value corresponding to twice the operating
value and inject the current instantaneously. The operating time measured by the timer should
have a deviation of less than 3% of the set value or
10 ms (DEFT). Accuracy for inverse time
characteristics refer to IEC 255-3.
Repeat the test on the other phases or with the inverse time characteristics in the similar manner.
In case of inverse time characteristics the injected current should be selected according to the
characteristic curve, e.g. two times I
S
. The tripping time may be red from the characteristic curve
diagram or calculated with the equations given under "technical data".
Please observe that during the secondary injection test the test current must be very stable, not
deviating more than 1%. Otherwise the test results may be wrong.
7.4.4
Checking the high set element of the relay
Set a current above the set operating value of I>>. If required an alarm relay can be tripped if in this
moment if it is assigned to this function. Check the tripping time of the high set element according
to chapter 7.4.3.
Check the accuracy of the operating current setting by gradually increasing the injected current un-
til the I>> element picks up. Read the current value from the ammeter and compare it with the de-
sired setting.
Repeat the entire test on other phases and earth current input circuits in the same manner.
Note !
Where test currents >4 x I
N
are used, the thermal withstand capability of the current paths has to be
considered (see technical data, chapter 8.1).